batteries are still being made by the factory for Toyota, they own a major % of it, they produce the gm pack as well. dealers might fight you about it, but I'm told if you place the order about 3 weeks a new pack shows up. price I've heard is 4k plus 1k core charge. no clue on install. it is a complete pack, so while heavy, it's like 4 bolts, one plug and 2 wires to swap.
aftermarket green bean will come to you and swap out the battery with a refeb cell battery. last I saw posted was 2700 total. these hybrid batteries take the same cells as a prius, just more of them. they will. pretty much never be hard to get.
you can also buy 2 used prius packs and build one of ours with left overs if you're really diy.
there's a company selling lithium cells as well, bit unproven, but interesting enough. priced in the middle.